Project Summary Title: Understanding the Importance of Place of Birth on Alzheimer's Disease Outcomes in the US and UK Substantial geographic disparities in old age cognitive health and Alzheimer's Disease and Alzheimer's Dis- ease Related Dementia (AD/ADRD) diagnosis and mortality outcomes are well documented. Previous studies have linked old age cognitive health and AD risk to contemporaneous geographic, often neighborhood, con- texts. However, by old age, over a third of the US population has left their state of birth and an even greater share has left their county of birth, leaving the interpretation of contemporaneous links between geography and health clouded by endogenous mobility and disregarding the importance of childhood exposures in producing the geographic disparities in health across the life course and into old age. Successfully unraveling the im- portance of life course exposures and decisions in producing geographic disparities in health at old ages has the potential to contribute to basic science as well as policy, but efforts have been hampered by a lack of large datasets with place of birth information. Our proposal takes advantage of newly available data on place of birth for millions of UK and US born individuals across the early to mid 20th century combined with our team's inter- disciplinary background in life course demography, economics, biostatistics, population health, and epidemiol- ogy of old age morbidity and mortality processes. Our overall aim is to uncover the extent to which place of birth has contributed to old age cognitive health and AD/ADRD diagnosis and mortality disparities in the US and UK and to explore the mechanisms underlying these relationships. Our research team will leverage newly released data on millions of individuals across multiple datasets containing rich measures of health processes in old age and mechanisms of early contextual disadvantage and life course mobility. Using these data, we will pursue the following aims: (1) Create an ?Atlas of Birth of Place Impacts on AD/ADRD Outcomes? (2) Uncover mechanisms linking the relationship between place of birth and later health by focusing on mobility and early exposures. Together, these aims will allow a paradigm shift in how we understand old age health processes by integrating life course and spatial analysis into large scale analyses of the patterns and mechanisms of old age cognitive health and AD/ADRD diagnosis and mortality outcomes.